Valveless micropumps are widely used due to simple structure, durability and low maintenance. Understanding the fluid-membrane interaction and performance criteria is still a challenging problem for the scientists. In this work, a new model for side mounted valve micropumps is developed to obtain dynamic response of micropump with respect to piezoelectric actuation. The parameters of this model are obtained in terms of actuation frequency and geometrical dimensions of the micropump. Balancing elastic, inertial and damping forces result in the governing equation of the micropump system model. Analytical studies for the bottom mounted valve micropump indicate pump flux is independent of the chamber geometrical aspect ratio while, for the side mounted valve micropumps, geometric aspect ratio is an important factor in the net flux. Findings indicate there exists a peak excitation frequency at which the flux is maximum. As the excitation frequency increases beyond the peak frequency, the pump flux decreases sharply. This is due to enhancement of the fluid inertial forces. By increasing the aspect ratio of the chamber the maximum net flux raises considerably. While, increasing membrane to valve area ratio has adverse effect on the pump efficiency. Findings show that good agreement exists between the net flux response to actuation frequency obtained from modeling and experiment.